The objective of this work is to study the DNA replication of polyoma in vitro. Emphasis will be put on the isolation and characterization of cellular functions, of cytoplasmic and nuclear origin, required for viral DNA replication. In addition, the purification of polyoma T-antigen will be pursued, and the influence of this viral function on the initiation of new rounds of replication in vitro will be studied. BIBLIOGRAPHIC REFERENCES: Francke, B., and T. Hunter. In Vitro Polyoma DNA Synthesis: Requirement for Cytoplasmic Factors. J. Virology, 15, 97-107 (1975); Hunter, T., and B. Francke. In Vitro Polyoma DNA Synthesis: Inhibition by 1-beta-D-Arabinofuranosyl CTP. J. Virology, 15, 759-775 (1975).